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1:9 Scale B-17G - 'Sweet Pea'

wilmracer

I build things that fly (sometimes)
Mentor
I don't have an FT radial but if I got one I'd start with a setup that pulls around 1.2KW on 6s, then see how warm it gets. This is the same size motor as the Tacon Bigfoot 60, it just has a bit more KV so it should handle a few more watts.

My gestimation numbers say that on 6s the 16" 3 blades will be dangerous and the 15" 3 blades will be borderline on the high end.

We'll have to see. I'll definitely test the 16", and likely test it cut down to 15 and maybe even 14". As for the 15x7x3 I'm thinking that right out of the box it may be just fine (although top end speed may be a bit lacking)

Below is chart that @willsonman did when he tested an early version of the motor. the 13x8x3 really didn't draw that much in terms o amps. About 1500ish with a theoretical top end in the mid 70s. The 15x10 still had some overhead in terms of Amps (and of course this was static). Cutting it to 14.5x10, with the extra blade, might put it in a sweet spot, but we'll have to see.

Again, it is a bomber and I shouldn't really ever need to fly at full power, but I do want to know that the power is there if I need it.

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Off to play in the shop a bit :)
 

wilmracer

I build things that fly (sometimes)
Mentor
Well.... I must have been tired when I glued those nacelle formers together last night and made a bonehead move, installing the center former upside down. I noticed this AM and I'm definitely annoyed. I MIGHT be able to remove and fix it, but TBH the right call will be to rebuild from scratch, making some adjustments along the way to work better with this build technique... So that will be this weekend's project. Like I mentioned above, the plans I'm playing with didn't account for retracts, so the "bay" where the gear goes and the wheel retracts into was going to be VERY tight. I measured and it would have worked, but I'm going to mod it a bit to get another 1/2" of space in there. I'll also tweak the design for how it mates to the main spar and how the rotation plate for the trunion will be attached.

I THINK I'll actually build out the airworthy main gear and install them in the nacelles BEFORE attaching them to the wing, and might also get the motor mounts just right as well. It will be a lot easier to work on these sections before gluing them in to the big wing.

The last purchase for parts was also made last night. Picked up some SERIOUS servos to drive the flaps. I'm using HS-5645MGs for most stuff (elevator halves, rudder, ailerons, steering, tailwheel retract) and those give a solid 168oz of torque @ 6v. That is more than enough for the "small" surfaces. The flaps are BIG though and at full deflection will see a ton of force. Got a pair of HS-7955TGs for those. Less than .09oz heavier than the 5646MGs but with Titanium gears and 333oz of torque @ 6v. I'm working on my plan to actuate the flaps but whatever I land on these servos will definitely hold up.
 

wilmracer

I build things that fly (sometimes)
Mentor
Rebuilt the inboard nacelles and started on outboard. A LOT of head scratching right now to get these right and get everything installed as far forward as possible. Inboard nacelles have more "heavy" ply to deal with landing gear forces. Outboard are mostly really light SIG plywood except for the firewall.

The remaining parts needed to mount the wing to the fuse showed up today. With the three day weekend I hope to have that done soon!
 

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wilmracer

I build things that fly (sometimes)
Mentor
Working out the centering/retention pins. This design is similar to the P40 but more robust due to the increased weight. I'm making some additional changes to my original plan but I think this will work great once everything is installed. I am currently thinking this large forward area will be ideal to install the sound system board, amp, and dedicated BEC. ESC extensions will likely route through the wire tubes as well, along with the extensions for the linear servos on the main gear.
 

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